Regenerative turbine fuel pumps are commonly used to pump fuel to an automotive engine since they have a higher and more constant discharge pressure than, for example, positive displacement pumps. In addition, regenerative turbine pumps typically cost less and generate less noise during operation. A problem develops, however, when the fuel temperature rises and fuel vapor bubbles form within the fuel. Such a result is common because fuel pumps are regularly mounted within a fuel tank where high fuel temperatures result from a variety of reasons, including, for example, hot fuel recirculated from fuel injectors in the engine, rotary motion of the pump impeller, or high ambient air temperatures. If the vapor bubbles thus formed are not removed, the pump flow rate decreases or the pressure drops, resulting in decreased pump efficiency. Fuel vapor also results in pump noise as the pump impeller rotates. If such vapor is not properly vented, annoying venting noises may occur.
A known method of removing the aforementioned fuel vapor bubbles is to provide a vapor purge orifice leading from the pumping chamber surrounding the impeller to the fuel tank, as in U.S. Pat. No. 3,881,839 (MacManus), so that the fuel vapor can bleed back into the fuel tank. Various designs have focused on different factors to optimize vapor venting. For example, placement of a fuel guide recess to direct vapor laden fuel to a purge orifice is disclosed in U.S. Pat. No. 5,160,249 (Iwai et al). In U.S. Pat. No. 5,024,578 (Vansadia), a regenerative fuel pump is vented by a V-shaped passage 84 and an arcuate annular duct 86 that terminate in a restrictor 88. Fuel vapors are vented from a fuel pump in U.S. Pat. No. 4,538,958 (Takei et al) by a passage 6 which communicates with the pump chamber and a housing 7 located over a passage 6. None of these disclosures, however, discuss the shape of the purge orifice.
U.S. Pat. No. 4,844,621 (Umemura et al) and U.S. Pat. No. 5,192,184 (Nobuo et al) show various embodiments of a purge channel and lengths therefore with emphasis on a single outlet. A U-shaped slot is disclosed in U.S. Pat. No. 4,793,766 (Kumata) for separating fuel vapor from liquid fuel in the pumping chamber, but not in the purge channel.
A problem with these prior art disclosures is that consideration is not given to the shape of the purge orifice through which the fuel must flow if it is to be purged at all. In addition, the purge channel of previous pumps has vented only through one vapor outlet thus failing to take advantage of the noise reduction benefits in dual outlet venting and in venting through a baffled channel.